This invention generally relates to a method of controlling a change in a torque value of a semi-automated vehicle transmission system using a two-stage process.
Vehicle transmissions are well known and include automatic, manual and semi-automatic types. Each of the transmission types have advantages that make them suitable for various applications. Heavy duty vehicles typically include a manual or, more recently, a semi-automatic transmission. Semi-automatic transmissions of various types have been proposed. The basic principal is to assist a driver in performing a manually selected gear ratio change using a system that is at least partially automated. While such transmissions have advantages, they are not without shortcomings and drawbacks.
For example, in a partially automated transmission at some point during a gear ratio change, the driver is precluded from controlling the engine and transmission. The transition from automated control back to driver control is often accompanied by less than desirable phenomena. For example, a change in torque value when returning control to the driver can result in wheel slip or a relatively abrupt change in vehicle wheel speed. Both of these conditions are potentially annoying or distracting to a driver of the vehicle and introduce potential undue wear on the transmission.
Therefore, it is desirable to provide a method of controlling torque changes in a vehicle transmission that results in a more smooth transition between operating states when returning control of the transmission and engine to the driver of the vehicle. This invention addresses those needs and provides an effective solution.